He closed New York Newsday. He sacked 700 at the Los Angeles Times. And on Sept. 7, Mark Willes shuffled top management at Times Mirror, ousting three senior executives. Wall Street loves his style: Times Mirror stock has soared nearly 70% since Willes was named president and CEO on May 1, to 30 1/2 on Sept. 13. Now comes the hard part: expanding the business after disbanding or paring electronic media, regional sections, Spanish-language editions, and other would-be growth vehicles.